From PC to MacBook - iTunes Match

Just changed from PC to MacBook.
Had already registered with iTunes Match when I had the PC and had all music stored on external hard drive.
Now I have the MacBook I have attached the external hard drive and pointed itunes to it which added all the music to the library no problem.
What happens with iTunes Match now? When I go to match its asked me to subscribe again rather than add computer. My library won't be duplicated will it?
I just want this to be my main source for itunes as I need to update some of the artwork etc.
Any help would be greatly appreciated,
Tanks.
Nick

Having gone into it again and clicked subscribe it recognised that I already have an account and added the computer and scanned/matched it. I was also not getting the "update iTunes match" within the store menu at the top. All seems fine now and computer matched, update option has now appeared as well.
Basically I was worried that as I used my old computer as my primary source and then changed to macbook it would mess it up, should have had more faith in Apple, they seem to think of everything.
Thanks for your help anyway.